<!DOCTYPE html>
<html>
<head>
	<title></title>
	<style>
		
	</style>
</head>
<body>
	<button onclick="start()">开始</button>
	<div id='box'>10</div>
</body>
	<script>
		var num=10;

		function start(){
			if(num<=0)
			{
				return;
			}
			setTimeout(start,100);
		}

	</script>
</html>